﻿<p>An <em>IfcPropertyDependencyRelationship</em> describes an identified dependency between the value of one property and that of another.</p>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC2x2
</blockquote>

<blockquote class="change-ifc2x4">
IFC4 CHANGE&nbsp; Made subtype of <em>IfcResourceLevelRelationship</em> (attribute order changed).
</blockquote>

<p class="use-head">Use Definition</p>
<p>Whilst the <em>IfcPropertyDependencyRelationship</em> may be used to describe the dependency, and it may do so in terms of the expression of how the dependency operates, it is not possible through the current IFC model for the value of the related property to be actually derived from the value of the relating property. The determination of value according to the dependency is required to be performed by an application that can then use the Expression attribute to flag the form of the dependency.</p>